Dam operators trusted 'professional judgment' in flood

QUEENSLAND dam engineers relied on their "professional judgment” in predicting peak water levels during the state's devastating 2011 flood emergency, a court has heard.

The NSW Supreme Court is hearing a class action against the Queensland Bulk Water Authority trading as Seqwater on behalf of more than 6000 flood victims impacted by the destructive weather event in January 2011.

The plaintiffs claim operators of Wivenhoe and Somerset dams failed to follow their operations manual in the emergency and didn't adequately take account of rain forecasts at the time.

A central issue is whether any failures on these points led to water being released from the dams too late, causing unnecessary flooding and damage in Brisbane and southeast Queensland.

On Monday, counsel for Seqwater, Brian O'Donnell QC, defended the actions of flood engineers working on January 7 as the crisis developed.

Mr O'Donnell said rain forecasts issued on that day predicted 10-25 millimetres to fall in both Wivenhoe and Somerset dam catchments on January 8, 25-50mm in Wivenhoe and 50-100mm in Somerset on the 9th, and 25-50mm in Wivenhoe and 50-100mm in Somerset on the 10th.

He told the court that, given the "PME forecast”, the flood engineer on duty "had no expectation that Wivenhoe would reach 68.5 (metres height)”.

"He says it was his professional judgment that the peak level would not reach 68.5,” Mr O'Donnell said on the second day of his opening address.

"He also says that rainfall had been mild in the last 24 hours.”

Mr O'Donnell said the engineer also "did a model run” during his shift showing the expected level at Wivenhoe "would be less than 68.5”.

In the days that followed, he said the actions of engineers working 12-hour shifts "in the heat of the event” also showed concern for forecasts.

"Their particular concern was the prospect of heavy rain falling downstream of the dam,” Mr O'Donnell told the court.

The trial has previously heard plaintiffs' claims that flood engineers were "blinkered” in their approach to managing the crisis and that their actions were contrary to common sense.

It has been told that on January 11, at the height of the crisis, the rate of release at the Wivenhoe dam was more than 7400 cubic metres per second, a sharp increase from about 1400 cubic metres per second the day before.

The floods - already the subject of a 2012 commission of inquiry - caused hundreds of millions of dollars in damage across Queensland.